Electrochemical etching apparatus

ABSTRACT

An electroplating etching apparatus includes a power to output current, and a container configured to contain an electrolyte. A cathode is coupled to the container and configured to fluidly communicate with the electrolyte. An anode is electrically connected to the output, and includes a graphene layer. A metal substrate layer is formed on the graphene layer, and is etched from the graphene layer in response to the current flowing through the anode.

DOMESTIC PRIORITY

This application is a continuation of U.S. patent application Ser. No.14/666,876, filed Mar. 24, 2015 which is a continuation-in-part of U.S.patent application Ser. No. 13/617,727, filed Sep. 14, 2012, which isnow U.S. Pat. No. 9,045,842, issued Jun. 2, 2016, the disclosures ofwhich are incorporated by reference herein in their entirety.

GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.:FA8650-08-C-7838 awarded by Defense Advanced Research Projects Agency(DARPA). The Government has certain rights in this invention.

BACKGROUND

The present disclosure generally relate to electroplating, and morespecifically, to electrochemical etching of metal substrates.

The use of graphene in electronic devices and semiconductor applicationshas increased in recent years due to the desirable properties grapheneoffers. For example, graphene has remarkable electrical propertiesincluding impressively high current density, mobility and saturationvelocity, and 2D geometry of graphene also makes it compatible to theconventional CMOS top-down process flow. Thus, it has become desirableto incorporate graphene into semiconductor devices.

A growing trend for producing graphene is the use of chemical vapordeposition (CVD) of hydrocarbons to synthesize graphene films on metalsubstrates, especially copper foils. Thereafter, the metal substrate maybe removed and the graphene may be transferred to another dielectricsubstrate. The conventionally accepted means for removing the metalsubstrate from the graphene is to immerse the graphene/metal substratein a chemical etchant to dissolve the metal. However, the dissolvedmetal by-product causes environmental pollution and increases productioncosts incurred from having to properly dispose of the metal by-product.

SUMMARY

According to an exemplary embodiment of the present disclosure, anelectroplating etching apparatus comprises a power supply including anegative terminal and a positive terminal configured to output current,a container configured to contain an electrolyte, a cathode coupled tothe container and configured to fluidly communicate with theelectrolyte, the cathode having a portion electrically connected to thenegative terminal of the power supply; and an anode having a portionelectrically connected to the positive terminal of the power supply, theanode including a graphene layer and a metal substrate layer that istransferred to the cathode in response to the current flowing throughthe anode.

In another exemplary embodiment of the present disclosure, an anodeconfigured to electrically communicate with an electrochemical etchingapparatus. The anode comprises a graphene layer including a firstsurface and a second surface opposite the first surface, a metalsubstrate layer contacting the first surface and configured toelectrically transfer from the graphene layer to a cathode in fluidcommunication with an electrolyte in response to a current flowingthrough the anode, an electrically conductive polymer formed on thesecond surface of the graphene layer, and a metal plate having a firstportion in electrical communication with the electrically conductivepolymer and a second portion in electrical communication with thepositive terminal of a power supply to receive the current.

In yet another exemplary embodiment of the present disclosure, anelectrochemical etching method comprises forming an anode having agraphene layer formed on a metal substrate layer, disposing the metalsubstrate layer in an electrolyte, disposing a cathode beingelectrically connected to the negative terminal of the power supply inthe electrolyte, and connecting at least one of the graphene layer andthe metal substrate layer to a power source to supply the currentthrough the anode and the electrolyte such that the metal substratelayer is etched from the graphene layer and transferred to the cathode.

In still another exemplary embodiment according to the presentdisclosure, a method of forming an anode. The method comprises forming agraphene layer on an upper surface of a metal substrate layer, the metalsubstrate layer configured to fluidly communicate with an electrolyte,forming an electrically conductive polymer on a first surface of thegraphene layer opposite the lower surface of the metal substrate layer,and forming a metal plate in electrical communication with theelectrically conductive polymer, the metal plate configured toelectrically communicate with the positive terminal of a power supply toreceive the current such that the metal substrate layer is transferredto a cathode in fluid communication with the electrolyte viaelectrodeposition.

Additional features and utilities are realized through the techniques ofthe present disclosure. Other exemplary embodiments and features of theclaimed disclosure are described in detail herein and are considered apart of the claimed disclosure. For a better understanding of thepresent disclosure and corresponding features, descriptions of theexemplary embodiments are presented below.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the present disclosure isparticularly pointed out and distinctly claimed in the claims at theconclusion of the specification. The forgoing and other features, andutilities of the present disclosure are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 illustrates an electrochemical etching apparatus according to anexemplary embodiment of the present disclosure;

FIG. 2 is a flow diagram illustrating a method etching a metal substratelayer from a graphene layer according to at least one exemplaryembodiment of the present disclosure;

FIG. 3 illustrates an anode configured to electrically communicate withan electroplating etching apparatus according to an exemplary embodimentof the present disclosure;

FIG. 4 is a process flow illustrating formation of the anode illustratedin FIG. 3; and

FIG. 5 is a flow diagram illustrating a method of forming an anodeillustrated in FIGS. 3-4 according to at least one exemplary embodimentof the present disclosure.

DETAILED DESCRIPTION

Referring now to FIG. 1, an electroplating etching apparatus 100according to an exemplary embodiment of the present disclosure isillustrated. The electroplating etching apparatus 100 includes a powersupply 102, a container 104 and an electrical etching network 106. Theelectrical etching network 106 includes a cathode 108 and an anode 110,each in electrical communication with the power supply 102 as discussedin greater detail below.

The power supply 102 includes a negative terminal 112 and a positiveterminal 114 that outputs a current. The current may be a direct current(DC), and may have a value selected to achieve a current density at theanode ranging from about 2 mA/cm² to about 200 mA/cm².

The container 104 may contain an electrolyte solution 115 capable ofconducting a current that induces an electrochemical etching process toetch away a metal substrate formed on the anode 110. In addition, themetal substrate may be transferred from the anode 110 to a surface of acathode 108 disposed in the electrolyte solution 115 via anelectrodeposition process to effectively remove the metal substrate. Theelectrolyte solution 115 may comprise cupric ions and/or chlorine ionsthat render the electrolyte solution to be electrically conductive.According to at least one exemplary embodiment, the electrolyte solution115 includes, but is not limited, to sulfuric acid (H₂SO₄), coppersulfate pentahydrate, 2N hydrochloric acid, sodium sulfate, etc. Anelectrolyte solution of sulfuric acid may range from 2-50 grams/liter(g/L), copper sulfate pentahydrate may range from 20-300 g/L, 2Nhydrochloric acid may range from 0-5 milliliters/liters (ml/L), andsodium sulfate may range from 80-200 g/L. It can be appreciated thatother solutions of acids, bases or salts may be used as the electrolytesolution 115. In addition, the electrolyte solution 115 may compriseeither H₂SO₄ or chloride (Cl), and an electrolyte metal. The electrolytemetal may include, but is not limited to, copper and tin. Further, theelectrolyte metal may be matched to a metal substrate layer of the anode110. For example, if the metal substrate layer of the anode 108 is acopper substrate layer, the electrolyte solution 115 may be copperchloride (CuCl₂).

The electrical etching network 106 is in electrical communication withthe power supply 102 and in fluid communication with the electrolytesolution 115. More specifically, in at least one exemplary embodimentillustrated in FIG. 1, the cathode 108 may be coupled to an innersurface of the container 104 and immersed in the electrolyte solution115. An electrically conductive wire 114, for example, may have one endconnected to the cathode 108 and an opposing end connected to thenegative terminal 112 of the power supply 102. The cathode 108 may beformed of any metal configured to receive metal transferred from theanode 110 via an electroetching process, i.e., throughelectrodeposition. In at least one exemplary embodiment, the cathode 108is formed of copper (Cu). In another exemplary embodiment, the metal ofthe cathode 108 is matched to a metal substrate of the anode 110. Forexample, if the anode includes a copper metal substrate layer to beetched away, the cathode may be formed of copper.

The anode 110 is in electrical communication with the positive terminal114 of the power supply 102 via a second electrically conductive wire116. The anode 110 may include a graphene layer 118 formed on a metalsubstrate layer 120. In at least one exemplary embodiment the graphenelayer 118 may be synthesized on the metal substrate layer 120 using achemical vapor distribution (CVD) process. The wire 116 may beelectrically connected to a portion of the metal substrate layer 120and/or the graphene layer 118 using a polymer film 121, such as apolyethylene adhesive film. Further, the metal substrate layer 120 maybe disposed in fluid communication with the electrolyte solution 115.

An electrochemical circuit may be effected when the cathode 108 and theanode 110 are introduced to the electrolyte solution 115 as describedabove. Accordingly, the current output from the power supply 102 travelsthrough the anode 110 and to the electrolyte solution 115, which inducesan electrochemical etching process such that the metal substrate layer120 is etched away from the anode 110 and dissolved in the electrolytesolution 115. In another embodiment of the disclosure, the currentoutput from the power supply 102 may induce an electroplating processsuch that a metal substrate layer 118 formed on the anode 110 istransferred to the cathode 108 via electrodeposition. As a result, themetal substrate layer 120 is removed, i.e., etched, from the anode 110,leaving only the graphene layer 118, which may later be transferred toanother desired substrate, for example as silicon. While the metalsubstrate 120 layer is removed from the graphene layer 118 of the anode110, a new metal substrate is formed on the cathode 108 and regeneratedthereon. A new graphene layer may later be formed on the new metalsubstrate layer of the cathode 108 such that the metal substrate layermay be recycled. Further, the composition of the electrolyte solution115 may be maintained, thereby providing an environmentally-friendlysolution for disposing of the electrolyte solution.

Referring to FIG. 2, a flow diagram illustrates a method of etching ametal substrate layer from a graphene layer according to at least oneexemplary embodiment of the present disclosure. The method begins atoperation 200, where an anode is formed having a graphene layer formedon a metal substrate layer, such as copper In addition, a polymer filmmay be coated on graphene for mechanical support. At operation 202, themetal substrate layer is fluidly communicated with an electrolyte, suchas a H₂SO₄ solution. A cathode in electrical communication with thenegative terminal of the power supply is disposed in fluid communicationwith the electrolyte at operation 204. The anode is connected to a powersource to received current at operation 206. In response to the current,the metal substrate layer is etched from the graphene layer andtransferred to the cathode at operation 208, and the method ends.Alternatively, at least one embodiment of the disclosure provides afeature where the metal substrate layer may be etched from the graphenelayer and dissolved in an electrolyte solution without being transferredto a cathode. Accordingly, a graphene layer is obtained, which may betransferred to another desired substrate without relying on a chemicaletchant to dissolve the metal substrate layer.

Referring now to FIG. 3, an anode 300 configured to electricallycommunicate with an electroplating etching apparatus is illustratedaccording to at least one exemplary embodiment of the presentdisclosure. The anode 300 includes a metal substrate layer 302, agraphene layer 304, an electrically conductive polymer 306, and a metalplate 308.

The metal substrate layer 302 includes a first surface, such as a lowersurface, and an opposing second surface, such as an upper surface. Themetal substrate layer 302 is configured to fluidly communicate with anelectrolyte solution. The metal substrate layer 302 may include, forexample, a copper film layer. A graphene layer 304 may be formed on theupper surface of the metal substrate layer 302. As discussed in detailabove, when current flows through the anode 300 during an electroplatingprocess, the metal substrate layer 302 is transferred from the graphenelayer 304 to a cathode in fluid communication with an electrolytesolution via electrodeposition. As a result, the metal substrate layer302 is etched from the anode 300, thereby leaving only the graphenelayer 304. Thereafter, the graphene layer 304 may be transferred toanother desired substrate.

It can be appreciated that the anode 300 may be formed without theelectrically conductive polymer 306 and metal plate 308. In this case,however, the rate at which the metal substrate layer 302 is etched isproportional, i.e., dependent on, the remaining thickness of the metalsubstrate layer 302 since the current flows from the edge of the metalsubstrate layer 302 and graphene layer 304. More specifically, as themetal substrate layer 302 is etched and its thickness diminishes, thecurrent density realized by the graphene layer 304 increases and maybecome too large, thus damaging the graphene layer 304. To preventdamage, the current output from a power supply is kept low such that thecurrent density does not reach a level that damages the graphene layer304. However, the low current throughput may cause a residual amount ofmetal substrate layer 302 to remain on the graphene layer 304.

For example, in a case where a copper film 302 having a thickness of 100micrometers (μm) is used as the metal substrate layer 302, a low currentoutput from a power source needs be selected such that a current densityis kept at an accepted level. Accordingly, the graphene layer 304 is notdamaged as the copper film 302 is etched away. However, since thecurrent is low, a residual amount of copper film 302 may remain on thegraphene layer 304. As a result, the electroetching procedure isprolonged to ensure the copper film layer 302 is completely removed.

To overcome the dependency of the current flow on the size of the metalsubstrate layer 302, at least one exemplary embodiment of the presentdisclosure provides the electrically conductive polymer 306 and metalplate 308. The electrically conductive polymer 306 may couple thegraphene layer 304 to the metal plate 308. More specifically, theelectrically conductive polymer 306 is formed on a second surface of thegraphene layer 304 opposite the metal substrate layer 302. In at leastone exemplary embodiment, the electrically conductive polymer 306includes, but is not limited to, Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS). Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) is an electrically conductive polymerthat inherently has at least one ionomer. More specifically,Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) isan electrically conductive polymer mixture of two ionomers.

Other examples of electrically conductive polymers include, but are notlimited to, electrically conductive organic polymers, electricallyconductive semi-flexible rod polymers, electrically conductive polymerscomprising heterocyclic aromatic organic compounds, and electricallyconductive polymers comprising a polymerized thiophene.

For instance, the electrically conductive polymers include, but are notlimited to, Polyaniline (PAM), Polythiophenes (PTs), Polypyrrole (PPy),and Polyacetylene (Pa). Polyaniline (PAM) is an electrically conductiveorganic polymer comprising an electrically conductive semi-flexible rodpolymer. Polythiophenes (PTs) is an electrically conductive polymercomprising a polymerized thiophene having at least one delocalizedelectron along a conjugated backbone of the electrically conductingpolymer. The delocalized electron can be achieved, for example, byeither p-doping or n-doping the polymerized thiophene. Polypyrrole (PPy)is an electrically conductive polymer comprising a heterocyclic aromaticorganic compound. Polyacetylene (Pa) is an organic polymer comprising achain of carbon atoms with alternating single and double bonds betweenthem. Each carbon atom is bonded with a hydrogen atom. Alternatively,each carbon atom is bonded with a functional group.

At least one portion of the metal plate 308, such as a lower surface, iscoupled to the electrically conductive polymer 306. The metal plate 308may be formed of a metal including, but not limited to, gold, copper,silver and tin. Further, the surface area of the metal plate 308 may bematched to have the same surface area of the metal substrate layer 302and/or the graphene layer 304. A second portion of the metal plate 308,such as an upper surface, is in electrical communication with an outputof a power supply to receive an electrical current. For example, anelectrically conductive wire 310 having a first end may be connected tothe upper surface of the metal plate 308, and an opposite end may beconnected to the output of the power supply. Accordingly, current fromthe power supply may be delivered to the anode 300 and through the metalplate 308, the graphene layer 304 and the metal substrate layer 302 toan electrolyte solution. As a result, an electroetching process takesoccurs, which etches the metal substrate layer 302 away from thegraphene layer.

Therefore, since the first end of the wire 310 is connected to the metalplate 308, the current flows through the full surface of the graphenelayer 304 and the metal substrate layer 302, and a significantly highercurrent may be delivered through metal substrate layer 302 withoutdamaging the graphene layer 304. Accordingly, at least one exemplaryembodiment of the present disclosure provides an electroplatingapparatus where the etching time is independent from the remainingthickness of metal substrate layer 302, and the overall etching time maybe reduced.

Turning again to the case of the 100 μm thick copper film 302 discussedabove, since current flows through the full surface of the copper film302 instead of flowing from the edge of the copper film 302, asubstantially higher current can be applied while keep the same currentdensity without damaging the graphene layer 304. In one embodiment, forexample, the current density may be kept at 2 mA/cm². Accordingly, atleast one exemplary embodiment illustrated in FIG. 3 provides an anode300 including a graphene layer 304 electrically coupled to a metal plate308 configured to receive current and maintain a sustainably increasedcurrent throughput through the copper film 302. Therefore, the overalletching time of the copper film 302 may be reduced, and large scaleproductions of graphene may be achieved.

A method of forming an anode used by an electroplating etching apparatusaccording to at least one exemplary embodiment of the present disclosuremay be realized with reference to FIGS. 4 and 5. More specifically, FIG.4 is a process flow illustrating formation of the anode 300 illustratedin FIG. 3, and FIG. 5 is a flow diagram illustrating a method of formingan anode 300 configured for application with an electroplating etchingapparatus according to at least one exemplary embodiment of the presentdisclosure. At operation 500, a graphene layer 304 is formed on a metalsubstrate layer 302, such as a copper film. The graphene layer 304 maybe formed using various processes including, but not limited to,chemical vapor deposition (CVD). An electrically conductive polymer 306is formed on a surface of the graphene layer 304 opposite the surfacecontacting the metal substrate layer 302 at operation 502. At operation504, a metal plate 308 is coupled to the electrically conductive polymer306. Accordingly, the electrically conductive polymer 306 and thegraphene layer 304 are disposed between the metal substrate layer 302and the metal plate 308, and the method ends.

The terminology used herein is for the purpose of describing exemplaryembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the present disclosure. Forinstance, the operations may be performed in a differing order or stepsmay be added, deleted or modified. All of these variations areconsidered a part of the claimed embodiments.

While exemplary embodiments of the present disclosure have beendescribed, it will be understood that those skilled in the art, both nowand in the future, may make variations to the embodiments which fallwithin the scope of the following claims. These claims should beconstrued to maintain the proper protection of the embodiments of thedisclosure described herein.

What is claimed is:
 1. An electrochemical etching apparatus, comprising:a power supply including a negative terminal and a positive terminalconfigured to output current; a container configured to contain anelectrolyte; a cathode coupled to the container and configured tofluidly communicate with the electrolyte, the cathode having a portionelectrically connected to the negative terminal; an anode having aportion electrically connected to the positive terminal, the anodeincluding a graphene layer and a metal substrate layer, the anodefurther including a metal plate having a first portion in electricalcommunication with the positive terminal to receive the current; and anelectrically conductive polymer configured to couple the metal plate tothe graphene layer such that the electrically conductive polymer and thegraphene layer are disposed between the metal substrate layer and themetal plate.
 2. The electrochemical etching apparatus of claim 1,wherein the electrically conductive polymer comprises at least oneionomer.
 3. The electrochemical etching apparatus of claim 2, whereinthe electrically conductive polymer is a polymer mixture of twoionomers.
 4. The electrochemical etching apparatus of claim 3, whereinthe electrically conductive polymer comprisesPoly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). 5.The electrochemical etching apparatus of claim 1, wherein theelectrically conductive polymer comprises an electrically conductiveorganic polymer.
 6. The electrochemical etching apparatus of claim 1,wherein the electrically conductive polymer comprises a polymerizedthiophene.
 7. The electrochemical etching apparatus of claim 6, whereinthe electrically conductive polymer is either p-doped or n-doped.
 8. Theelectrochemical etching apparatus of claim 7, wherein the polymerizedthiophene includes at least one delocalized electron along a conjugatedbackbone of the electrically conducting polymer.
 9. The electrochemicaletching apparatus of claim 8, wherein the electrically conductivepolymer comprises Polythiophene (PT).
 10. The electrochemical etchingapparatus of claim 1, wherein a first surface of the graphene layer isdisposed on an upper surface of the metal substrate layer, and the metalsubstrate layer is configured to fluidly communicate with theelectrolyte.
 11. The electrochemical etching apparatus of claim 11,wherein the anode further comprises a metal plate having a first portionin electrical communication with the output of the power supply toreceive the current.
 12. A method of performing an electrochemicaletching process, the method comprising: disposing a cathode in fluidcommunication with an electrolyte; forming an anode including a graphenelayer formed on a metal substrate layer; coupling a metal plate to thegraphene layer via an electrically conductive polymer; disposing themetal substrate layer in an electrolyte connecting the cathode to afirst terminal of a power supply having a first polarity and connectingthe metal plate and the graphene layer to the power source to supply acurrent through the anode and the electrolyte such that the metalsubstrate layer is etched from the graphene layer.
 13. The method ofclaim 12, wherein disposing the electrically conductive polymer and thegraphene layer between the metal substrate layer and the metal platecauses a time period at which the metal substrate layer is etched fromthe graphene layer to be independent from a remaining thickness of themetal substrate layer.
 14. The method of claim 13, wherein theelectrically conductive polymer comprises an electrically conductivesemi-flexible rod polymer.
 15. The method of claim 14, wherein theelectrically conductive polymer comprises Polyaniline (PANI).
 16. Themethod of claim 13, wherein the electrically conductive polymercomprises a heterocyclic aromatic organic compound.
 17. The method ofclaim 16, wherein the electrically conductive polymer comprisesPolypyrrole (PPy).
 18. The method of claim 13, wherein the organicpolymer comprises alternating double and single bonds.
 19. The method ofclaim 18, wherein the organic polymer includes a carbon atom betweeneach double bond and single bond, each carbon atom bonded with afunctional group.
 20. The method of claim 13, further comprising:forming the cathode from a metal configured to receive metal substratematerial etched from the metal substrate layer; and transferring themetal substrate material etched from the metal substrate layer thecathode via electrodeposition in response to current flowing through theanode.